The present invention relates to distillation columns, absorption columns and similar apparatus in general, and more particularly to improvements in trays which are utilized in such columns to confine bodies of liquid media at different levels of the tubular housings or shells of the columns. Still more particularly, the invention relates to improvements in trays of the type wherein the bottom wall is formed with substantially circular openings for the passage of vapor and/or gases and wherein the bottom wall can carry a weir for the flow of liquid medium into the tray at the next lower level in the housing or shell of the respective column.
Trays of the above outlined character are utilized in columns wherein the descending liquid medium should be brought into intimate and large-area contact with ascending vapors or gases, especially wherein the liquid medium should be contacted by large quantities of vapors or gases with relatively small losses in the pressure of the ascending vapors and/or gases. Trays of the above outlined character are disclosed, for example, in German Pat. No. 12 53 672.
It is well known that the trays in the shell of a distillation or absorption column are prone to highly pronounced vibration during contact between the liquid medium and the ascending vapors and/or gases and, at certain amplitudes, such vibration can lead to the development of cracks, fatigue and rapid destruction of the trays as well as of the entire column. The problems which arise as a result of vibration of trays in distillation and absorption columns are discussed, for example, by R. J. P. Brierley, P. J. M. Whyman and J. B. Erskine in the article entitled "Flow-Induced Vibration of Distillation and Adsorption Column Trays", Third International Symposium on Distillation, 1979 (published by The Institution of Chemical Engineers, Rugby, United Kingdom, Volume I, pages 2.4/45 to 2.4/63). Reference may also be had to the article by G. H. Priestman, D. J. Brown and H. K. Kohler entitled "Pressure Pulsations in Sieve-Tray Columns", Third International Symposium on Distillation, 1979 (published by The Institution of Chemical Engineers, Rugby, United Kingdom, Volume I, pages 2.4/1 to 2.4/16).
Cracking, aging and/or other damage to trays and/or columns not only entails substantial production losses but also necessitates fresh investments in capital. Moreover, claims for damages by the purchasers of such columns can be ruinous to the manufacturer. In spite of the recognition and detailed discussion of the problem, the makers of such trays failed to find a solution mainly because the cause of pronounced vibrations was unknown and, therefore, it was impossible to forestall such vibrations by appropriate design of the trays prior to assembly of the columns. The only solution which was known to the makers of such equipment was direct experience with previously erected columns, the undertaking of remedial measures in erected columns, and copying of the thus modified columns. Thus, in the case of a new column not based on previous experience, the manufacturer was never sure that the column would not vibrate at an excessive amplitude such as would give rise to aging, cracking and other deleterious effects upon the useful life of the trays and of the entire column. Moreover, remedial measures to reduce or eliminate vibrations of trays in erected columns constitute a hit-and-miss proposition, primarily due to the lack of knowledge of exact causes of such vibrations and/or of reliable measures for their elimination.
Recent experiments have led to the discovery that, when a vapor or gas ascends through the circular apertures of a series of superimposed trays in the shell of a column which is operated in the normal way, the entire flow of vapor or gases through the bottom wall of a tray is composed of a plurality of jet type flow pulses with a duration ##EQU1## wherein .rho..sub.L denotes the density of the liquid medium, R is the radius of an aperture in the bottom wall of the tray and .sigma. is the surface tension of the liquid medium. It was found that such pulses induce pronounced vibrations of the trays.